Scientists studied two species of early humans, Australopithecus africanus, which lived in southern Africa around three million years ago, and Paranthropus robustus, which inhabited the same area about a million years later.

Researchers found that the diets of the two species were similar, though A. africanus may have eaten a greater share of tough foods, while P. robustus probably ate more brittle foods, such as seeds.

The key difference in their diets was in how they each adjusted in times of food scarcity, scientists found.

"The two species ate similar foods much of the time, but differed mostly at crunch times, when their anatomical differences allowed them to fall back on different less-preferred foods," said Peter Ungar, a study author and anthropology professor at the University of Arkansas in Fayetteville.

The research is described in tomorrow's issue of the academic journal Nature.

Overall Texture

Dental microwear analysis investigates the microscopic scratches and pits that form on a tooth's surface as a result of its use.

The method used in the new study provided a novel, three-dimensional look at microscopic surface wear.

The technique measures the height of tens of thousands, if not hundreds of thousands, of points on a surface, capturing its overall texture at the microscopic level.

"The closer you look, the more detail you see, and the larger the area appears," said Christopher Brown, a study co-author and professor of mechanical engineering at Worcester Polytechnic Institute in Massachusetts.